The present invention generally relates to engine fuel systems and, more particularly, to combustible fuel devices that generate combustible vapors such as internal combustion engines.
Heretofore, combustible vapors were directed into the cylinders of internal combustion engines using either carburetors or fuel injectors. Fuel injectors were either continuous or pulsed. The continuous fuel injectors directed the combustible vapor into an intake manifold, and when an intake valve opened, the vapor was drawn into the cylinder by the piston. The pulsed fuel injectors directed fuel vapor on command into either a region upstream of each intake valve or directly into the combustion chambers. Both of these fuel delivery systems are highly developed, well known, and have been in use for decades.
As environmental regulations become more and more stringent, there is an increasing need for more precise control of the fuel/air stoichiometry in the combustion chambers of an engine. Several problems continue to persist in conventional fuel delivery technology. For instance, if excessive fuel is used or too little air is mixed with the fuel, the amount of hydrocarbon emissions increases correspondingly. Also, for fuel injectors, the orifices change in size over time; they get larger due to mechanical wear and smaller due to clogging from both the constituents in the fuel and small particles that are not removed by the fuel filter. In addition, the requirement for more precise fuel and air metering to meet environmental and fuel economy regulations has caused both carburetors and fuel injectors to become more and more expensive.
There is also a need for an inexpensive, simple fuel delivery system for small industrial engines, those having about twenty-five horsepower or less. These are the engines used on lawn mowers, rotary tillers, outboards and scooters, for example. These engines are increasingly being subject to environmental regulation, but it is impractical to incorporate a conventional fuel delivery system that costs as much or more than the rest of the machine.
Further, with these conventional fuel delivery systems, reliability continues to be a problem. For example, a conventional fuel injection system requires high-pressure pumps and carefully engineered fuel conduits, tubing, and connections that must withstand constant vibration and extreme variations in operating temperature.
It is apparent from the foregoing that although there are well-developed engine fuel delivery systems, there is a need for an approach that meets increasingly stringent environmental regulations, is reliable and inexpensive, and more precisely controls the fuel-air stoichiometry in combustion chambers.
Briefly and in general terms, an apparatus according to the invention includes (i) a drop ejector capable of discretely ejecting a combustible liquid in a digital manner, and (ii) a means for providing a pulse-modulated control signal to said drop ejector, wherein said pulse-modulated control signal is indicative of a desired number of drops to be ejected from said drop ejector within a given time frame.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.